This invention relates to methods for leak testing cavities in test items and, more particularly, to such methods in which the leak testing is accomplished by monitoring the rate of flow of pressurizing gas into the cavity.
Production line leak testing of items such as refrigeration systems is being continually challenged to keep pace with contemporary manufacturing strategies and technologies. New requirements often include increased quality and safety considerations, low cost or improved performance parts with thinner sections that are more susceptible to leakage, and increased production rates requiring shorter test cycle times.
Most previous production line leak detection methods require pressurization of the test item with a gas or liquid. After a stabilization period, the leak is measured by detecting the presence of the leaking gas, sensing pressure decay, or measuring gas flow necessary to maintain the system pressure. Typical leak detection systems employ one of two fundamental measurement techniques: pressure decay detection or steady-state flow detection.
In pressure decay detection, a test item is pressurized by connecting it to a gas pressure source. When the test item has reached a predetermined pressure, the test item is isolated from the source. After this point, a leak in the test item will produce a drop or decay in the test item pressure. If the volume of the test item is known, the amount of decay in the pressure can be used to calculate the magnitude of the leak. Although this method has significant utility, it may include false pressure decays from adiabatic or thermal changes in the test item.
In the steady-state flow detection test method, the test item is also connected to a gas pressure source. In this method, however, the source pressure is not isolated from the test item at any time during the test sequence. When the test item has been pressurized to reach a steady-state condition with the source pressure, any subsequent gas flow into the test item will be due to a leak in the test item. This gas flow can be measured using a gas flow meter and is representative of the flow rate of the leak. Steady-state flow detection may require excessive time for the test item to reach the required steady-state condition.
Pressure decay detection and steady-state flow detection both require the pressurization and stabilization of the test item prior to monitoring for a leak. A test item must be at a stable preset pressure before pressure decay detection or steady-state flow detection can begin. After the test item pressure has stabilized, the flow or pressure can be sampled to detect if the test item has an excessive leak. The required pressurization and stabilization result in significantly long test sequences that can slow the production rate of the test items. An object of the present invention is a significant reduction in time required to perform leak testing of cavities in test items.